The present invention pertains to a piston injection pump, and particularly, to means for gaining access for replacement of piston seals therein.
Injection molding apparatus for use in, for example molding polyurethane products, include reservoirs of component liquid materials supplied to an injection cylinder for the high pressure injection of such chemicals into a mixing head for subsequent injection into a mold for making articles. In such systems, the piston assembly for injecting the liquid into the mixing head develops pressures in the range of 2,000 to 3,000 pounds and is hydraulically driven. When it is necessary to replace the seals of the high pressure injection piston, typically, it has been necessary to disassemble the piston cylinder for removal of the piston head such that the seals can be replaced. With the prior art systems, the injection piston, typically, must be withdrawn through an access opening at one end which exposes it to the hydraulic fluid as well as depositing corrosive chemicals within the hydraulic cylinder. As a result, both cylinders and the piston need to be carefully cleaned which even requires additional time for seal replacement. Frequently, this required up to a day which naturally rendered the injection apparatus inoperative preventing use of up to several mixing heads in a given facility.
Further, typically the diameter of the hydraulic and injection pistons are identical. Since the amount of chemicals metered out by the pump is the same as the hydraulic fluid used to move the hydraulic piston and is at the same pressure, precise hydraulic pump fittings are required to assure accurate chemicals pumping.